One of the roles vitamin C has is as an antioxidant, protecting cells from oxidative stress. According to research appearing in Free Radical Research (1995;22(2):131-143), patients with inflammatory bowel disease (Crohn’s disease or ulcerative colitis) have reduced levels of vitamin C in the intestinal lining. Patients with Crohn’s disease have levels that are 35% below normal and patients with ulcerative colitis have levels that are 73% below normal. The researchers state that most of the loss of vitamin C is due to oxidative stress from inflammatory cells. The loss of vitamin C makes the cells lining the intestines more vulnerable to oxidative stress.

Research appearing in the Journal of Manipulative and Physiologic Therapeutics (1999;22(8):530-533) looked at the effect vitamin C supplementation had in students between the ages of 18 and 32 with a respiratory infection. The test group, consisting of 252 students received 1000 mg of vitamin C for the first six hours of the infection and 1000 mg of vitamin C three times each day following the initial dose. A control group, consisting of 432 students, was given decongestant medication and pain relievers. Overall, reported flu and cold symptoms in the test group decreased 85%, but not in the control group. Vitamin C supplementation was shown to be effective in relieving the symptoms of a respiratory infection.

Research appearing in the Archives of Internal Medicine (2008 July 28;168(14):1493-9) shows that higher levels of serum vitamin C is associated with a lower incidence of type 2 diabetes. Subjects of the study were over 21,000 non-diabetic patients.

A study appearing in BMC Gastroenterology (2009; 9(1): 74) looked at vitamin C supplementation and its relation to the development of gallstones. In the observational study involving 2,129 subjects between the ages of 18 and 65, it was found that supplementation with vitamin C reduced the chance of developing gallstones.